Code-quality review found 2 Important + 2 Minor issues; applied all 4:
- separator style: ────── → ============ (file convention)
- restored split sub-headers: outputs (6) / Welford state (4)
- restored full safety-net comment with issue #4 reference
- added inline value hints on every constant (per spec block)
Zero functional change — comments and whitespace only.
6353deed15